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A month ago, a $335 million federal grant for the Allston I-90 Multimodal Project, almost entirely filled a crucial funding gap for the once-in-a-generation undertaking.

Now – after a decade of slogging forward, and with an unpopular proposal for a rail layover scrapped — the transformative $2 billion highway and transit project set to realign the Massachusetts Turnpike in Allston is under a deadline and “on a roll,” according to advocates and officials involved in planning.

Over the last three weeks, the state has decided to nix a commuter rail layover yard from the design, making the project cheaper and easier to build, and has committed to replacing the Cambridge St. overpass, a bridge cutting over the Pike to connect pedestrians and vehicles from Lower Allston to Brighton.

Officials also face a hard deadline: they must conduct environmental planning, finalize a design, and get approval for permits by September 2026 as a condition of the federal funding.

“There’s nothing like a deadline to concentrate the effort,” said Tom Nally, planning director at A Better City, a local business association.

At a public meeting Wednesday night in Cambridge, state officials presented proposals for the parkland and shoreline that will open up following the realignment, including filling in the riverbank to varying degrees or constructing a boardwalk or sea wall, and different ways of managing stormwater runoff.

While the project initially aimed to replace the crumbling viaduct that carries the Mass. Pike, it has grown to include alternative modes of transportation: a new commuter rail station, bus and bike lanes, pedestrian walkways, and newly accessible parts of the riverbank.

The wide array of constituencies impacted by the project was evident at the Wednesday meeting, which highlighted the potential impacts on the health and shoreline of the Charles River.

Rowers, bikers, boaters, environmental advocates, and others grilled state officials on topics ranging from the aquatic and land habitats affected, to the potential dangers of new structures like a boardwalk, or how much “fill” might go into the river.

As it solicits public engagement from residents and advocates — and lobbying from influential institutions like Harvard — the state must juggle many competing priorities in deciding a final design for the project.

As it stands now, the realignment would bring 12 lanes of traffic across the turnpike and Soldiers Field Road down to ground level. Still, many advocates pressed the state to reduce the number of lanes on the road to make room for alternative modes of transit — though the state has largely resisted the idea so far.

Cole D. Rainey-Slavick, a Somerville resident, said the state’s lack of interest in cutting lanes clashed with their climate goals and professed commitments to reducing car-dependency across Massachusetts.

Rainey-Slavick said “every other conceivable use” of the river and its shore — from boating to managing runoff — “all have to make compromises because the giant elephant in the room: the 12 lanes of highways cannot be reduced.”

“The car is still king in Boston,” he added in an interview after the meeting.

Like many other participants, Jennifer Pieszak, a member of Community Rowing, saw room for improvement in the project.

“It’s supposed to be multimodal, and it seems very car centric,” she said in an interview. She added that the source of the federal funding, the federal Reconnecting Communities and Neighborhoods Grant Program, was intended for projects “to undo the wrongs” of highway construction, which broke up many urban neighborhoods in the mid-1900s.

According to the US Department of Transportation website, the RCN funding is meant for projects that work “by removing, retrofitting, or mitigating highways or other transportation facilities that create barriers to community connectivity.”

State Senator William N. Brownsberger ’78, whose district encompasses Allston-Brighton, said motorists had already accepted a compromise by seeing the lanes shrunk in size, if not in number.

In an emailed statement, Jacquelyn Goddard, a spokesperson for the Massachusetts Department of Transportation, said that a 2022 analysis predicted multiple negative impacts in the event of a lane reduction.

“Lane reductions would increase congestion by several hours daily, would lead to more traffic on neighborhood streets, would decrease the air quality, and would increase travel times for emergency vehicles,” Goddard wrote.

She added that the project team welcomes community feedback and is “working with project stakeholders to finalize a project finance plan to support the full multimodal project.”

—Staff writer Jack R. Trapanick can be reached at jack.trapanick@thecrimson.com. Follow him on X @jackrtrapanick.